1. Field of the Invention
The present invention relates to an endoscope system, a processor device, and a method for operating an endoscope system, capable of enhancing tissue structure such as blood vessels with the use of narrowband light in observation.
2. Description Related to the Prior Art
In a medical field, diagnosis using an endoscope system, which comprises a light source device, an endoscope device, and a processor device, is commonly performed. The diagnosis using the endoscope system includes normal observation, in which broadband light such as white light is used to observe an observation object in its entirety, and narrowband light observation, in which narrowband light of specific wavelengths is used to enhance tissue structure such as blood vessels and ductal structure.
In the narrowband light observation, blue narrowband light is used to enhance superficial blood vessels located in superficial tissue of the observation object. In addition, green narrowband light is used to enhance middle-layer blood vessels located in tissue in a middle layer of the observation object. A blue image signal, which is obtained by imaging the observation object under the blue narrowband light, is assigned to B and G channels of a monitor and a green image signal, which is obtained by imaging the observation object under the green narrowband light, is assigned to an R channel of the monitor (for example, see U.S. Pat. No. 8,216,126 corresponding to Japanese Pat. No. 4709606). Thereby, the superficial blood vessels and the middle-layer blood vessels are displayed in different colors. This makes it easy for a doctor to distinguish between the blood vessels in different layers.
It is generally known that human eyes have high sensitivity to differences in brightness (intensity) in an image, but low sensitivity to differences in color. In a case where the superficial and middle-layer blood vessels are displayed in different colors, the difference in depth between the superficial and middle-layer blood vessels may not be perceived accurately. For this reason, it is desirable to display the superficial and middle-layer blood vessels, which differ from each other in depth, with different brightness instead of different colors.